Recently, in the medical field, due to the rapid development of high-performance image capturing apparatus (or modality) and dose reduction technology, the number of medical images that can be acquired per each examination process has been increasing. However, since such an increased number of acquired medical images results in a vast amount of data that must be handled by an overall medical diagnostic system, problems arise such as a sharp increase in the cost of data storage and transmission. It is effective to reduce the amount of data to be handled by performing an image compression process on the medical images before the medical images are transmitted or saved (see Japanese Laid-Open Patent Publication No. 2003-126046). Various technologies for increasing the efficiency with which images are compressed have been proposed in the art.
According to Japanese Laid-Open Patent Publication No. 2009-291280, there have been proposed a system for and a method of sorting a sequence of cross-sectional images along a direction in which pixels of the images change. Then, the sorted images are regarded as a moving image, and an image compression process is performed thereon.
According to Japanese Laid-Open Patent Publication No. 2005-245922, a method and an apparatus have been proposed in which blocks of image data concerning pixels that share positions are encoded, and thereafter, the encoded blocks are sorted into groups in order to compress the image data.